The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Hybrid drive powertrains are known including a plurality of torque generative devices. For example, a powertrain can include an internal combustion engine and an electric motor, and the engine and the motor can be controlled to increase an overall efficiency of the vehicle, for example, by utilizing the motor in operation efficient for the motor, utilizing the engine in operation efficient for the engine, utilizing both devices to cooperatively provide torque when such operation is efficient, and utilizing the motor to regenerate energy to an energy storage device, for example, during braking of the vehicle or by drawing torque from the engine.
In an exemplary configuration, the engine and the motor each provide a torque to the powertrain. In another exemplary configuration, the engine supplies a torque to the motor, and the motor in turn supplies a torque to the rest of the powertrain.
Shutting down the engine when it is not being used saves fuel that would be consumed by otherwise idling or running the engine at low speed. When the engine is shut down, a shaft leading from the engine to the powertrain will either cease turning, requiring the rest of the powertrain to adjust for the unmoving shaft, or the rest of the powertrain must supply a torque to turn the shut down engine, overcoming the torque (due to friction, cylinder pumping forces, etc.) required to turn the engine. A clutch device may be employed between the engine and the rest of the powertrain to permit the engine to remain shut down and remain stopped while the rest of the powertrain continues to function.
Clutch devices or clutches are used to selectively connect or disconnect shafts capable of transmitting torque. Clutches can be hydraulically actuated. An exemplary shift between states controlled by a pair of clutches requires that one clutch be unloaded, permitting two shafts that were previously coupled to spin freely of each other, and subsequently that another clutch be loaded, coupling two shafts that were formerly decoupled or free to spin relative to one another. Hydraulically actuated clutches frequently include clutch plates that are spring loaded to a default decoupled position, wherein hydraulic pressure applied to a piston applies pressure that overcomes the bias of the spring to bring the plates to a coupled position.
Engines can include a dedicated starter motor which supplies a torque to the engine in order to crank the engine during start. Torque to start the engine can be drawn from the powertrain or the associated motor of the powertrain. A hybrid drive powertrain can include a plurality of motors wherein one motor can be used to provide a torque to the rest of the powertrain to propel a vehicle, while the other motor can be used to start the engine.